Women who recently took a certain formulation of birth control pills may have an increased risk of breast cancer, according to a new study published in the journal Cancer Research.
Researchers at the Fred Hutchinson Cancer Research Center and the University of Washington in Seattle reviewed health records for oral contraceptive usage among more than 1,100 women with beast cancer, most of whom were diagnosed with the disease in their 40s.
Researchers divided the birth control pills into three categories – those with a low level of synthetic estrogen (about 20 micrograms of ethinyl estradiol), those with a moderate level of estrogen (about 30 to 35 micrograms of ethinyl estradiol or 50 micrograms of mestranol), and those with high levels of estrogen (50 micrograms of ethinyl estradiol or 80 micrograms of mestranol.
The data showed that women who recently took high-estrogen pills were 2.7 times more likely to have breast cancer, and women who took moderate-estrogen pills were about 1.6 times more likely to have the disease. There was no increased risk for women who took the low-dose pills.
Researchers also found that pills containing ethynodiol diacetate, sold under the brand names Continuin and Femulen, carried a 2.6-fold risk, and triphasic combination pills containing 0.75 milligrams of norethindrone sold under the brand name Ortho 75, carried a 3.1-fold risk.
The results were not surprising, as they support previous studies, which have found a slight increased risk of breast cancer with use of some birth control pills.
The new study also shows that a woman’s cancer risk returns to normal when they stop taking the pills. The cancer risk was found only in women who had taken the pill within the previous year.
High estrogen birth control pills are also rarely prescribed in recent decades, since lower-dose pills have entered the market. Most women who use high dose estrogen pills have specific medical issues that necessitate the use of the drugs, for example if they have extreme breakthrough bleeding on lower estrogen formulations.
Previous studies have also shown that oral contraceptives offer a slight protection against ovarian and endometrial cancers, though with any medication patients should weigh the risks and benefits of a drug with their doctor.
Source: The Atlantic